85 lines
1.9 KiB
C++
85 lines
1.9 KiB
C++
#pragma once
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#include "bits.h"
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#include "helpers.h"
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#include <utility>
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namespace snmalloc
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{
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template<class T>
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class MPSCQ
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{
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private:
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static_assert(
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std::is_same<decltype(T::next), std::atomic<T*>>::value,
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"T->next must be a std::atomic<T*>");
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std::atomic<T*> back;
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T* front;
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public:
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void invariant()
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{
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#ifndef NDEBUG
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assert(back != nullptr);
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assert(front != nullptr);
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#endif
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}
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void init(T* stub)
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{
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stub->next.store(nullptr, std::memory_order_relaxed);
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front = stub;
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back.store(stub, std::memory_order_relaxed);
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invariant();
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}
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T* destroy()
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{
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T* fnt = front;
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back.store(nullptr, std::memory_order_relaxed);
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front = nullptr;
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return fnt;
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}
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inline bool is_empty()
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{
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T* bk = back.load(std::memory_order_relaxed);
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return bk == front;
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}
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void enqueue(T* first, T* last)
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{
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// Pushes a list of messages to the queue. Each message from first to
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// last should be linked together through their next pointers.
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invariant();
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last->next.store(nullptr, std::memory_order_relaxed);
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std::atomic_thread_fence(std::memory_order_release);
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T* prev = back.exchange(last, std::memory_order_relaxed);
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prev->next.store(first, std::memory_order_relaxed);
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}
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std::pair<T*, bool> dequeue()
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{
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// Returns the front message, or null if not possible to return a message.
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invariant();
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T* first = front;
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T* next = first->next.load(std::memory_order_relaxed);
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if (next != nullptr)
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{
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front = next;
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bits::prefetch(&(next->next));
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assert(front);
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std::atomic_thread_fence(std::memory_order_acquire);
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invariant();
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return std::pair(first, true);
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}
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return std::pair(nullptr, false);
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}
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};
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} // namespace snmalloc
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